1. Field of the Invention
The present invention relates to a communication system, and more particularly, to a communication system comprising one or more remote control transmitters and a single receiver disposed inside a mobile body such as a car wherein in response to reception of various kinds of switching information transmitted from a remote control transmitter, the receiver selectively controls a controllable device provided in the mobile body such as a car, depending on the kind of switching information received.
2. Description of the Related Art
A keyless entry system is a communication system which comprise one or more remote control transmitters and a single receiver disposed inside a mobile body such as a car wherein in response to reception of various kinds of switching information transmitted from a remote control transmitter, the receiver selectively controls a controllable device provided in the mobile body such as a car, depending on the kind of switching information received.
FIG. 5 is a simplified block diagram illustrating an example of such a keyless entry system disclosed in Japanese Examined Patent Publication No. 7-71337.
As shown in FIG. 5, this keyless entry system includes three, remote control transmitters 41-1, 41-2, and 41-3 and a single receiver 42 disposed inside a car.
The three remote control transmitters 41-1 through 41-3 each include: a transmitting circuit 43-1, 43-2, or 43-3 for generating a transmission signal; an identification data memory (ROM) 44-1, 44-2, or 44-3 for storing identification data R-1, R-2, or R-3 uniquely assigned to the respective transmitters 41-1, 41-2, and 41-3; and a transmitting antenna 45-1, 45-2, or 45-3.
The receiver 42 includes: a receiving circuit 47 for receiving a signal via a receiving antenna 46, amplifying the received signal, and further shaping the waveform of the amplified signal; a signal processing unit 48 for performing various control operations in various operation modes; a memory (EEPROM) 49 for storing the identification data R-1, R-2, and R-3; a setting switch circuit 50 including two switches 50-1 and 50-2 for setting the operation mode of the signal processing unit 48 to either a normal mode, writing mode, or an erasing mode depending on the on/off states of the switches 50-1 and 50-2; a door controller 51 for locking and unlocking the doors of the car; an indicator/alarm 52 including light emitting diodes and a horn, which operates when the operation mode is switched from the writing mode or the erasing mode to the normal mode; and a timer 53 provided in the signal processing unit 48.
The operation of the keyless entry system having the above construction is briefly described below.
First, the signal processing unit 48 in the receiver 42 is set in the normal mode. That is, the two switches 50-1 and 50-2 of the setting switch circuit 50 in the receiver 42 are both maintained in open states.
In this situation, if one of the three remote control transmitters 41-1, 41-2, 41-3, for example the remote control transmitter 41-1 is operated, the transmitting circuit 43-1 of the remote control transmitter 41-1 generates a control signal (FSK signal) containing a command of locking or unlocking a door of the car and also containing the identification data R-1 read from the identification data memory 44-1. The generated control signal is transmitted via the transmitting antenna 45-1 as a transmission signal at a radio frequency (RF).
In the receiver 42, the receiving circuit 47 receives via the receiving antenna 46 the transmission signal transmitted from the remote control transmitter 41-1. The received control signal is amplified and waveform-shaped, and then supplied to the signal processing unit 48. The signal processing unit 48 first compares the identification data R-1 contained in the received control signal with the identification data R-1 stored in the memory 49. If these data are identical, the signal processing unit 48 then detects the status of the door of the car via the door controller 51. If the door is in a locked state, then the signal processing 48 supplies a control signal to the door so as to unlock the door. On the other hand, if the door is in an unlocked state, then the signal processing unit 46 supplies a control signal to the door so as to lock the door.
When it is required to write identification data R-1, R-2, or R-3 into the memory 49, the switch 50-1 of the setting switch circuit 50 of the receiver 42 is closed by operator while maintaining the other switch 50-2 in the open state, so the operation mode of the signal processing unit 48 of the receiver 42 is set to the writing mode. And the timer 53 is started.
Immediately after setting the operation mode into the writing mode, if one of the three remote control transmitters 41-1, 41-2, 41-3, for example the remote control transmitter 41-1, is operated, a control signal containing the identification data R-1 read from the identification data memory 44-1 is generated by the transmitting circuit 43-1 of the remote control transmitter 41-1 and is transmitted as a transmission signal via the transmitting antenna 45-1. If the receiving circuit 47 of the receiver 4 receives the above control signal from the remote control transmitter 41-1, the receiving circuit 47 transfers the received control signal to the signal processing unit 48. The signal processing unit 48 detects the identification data R-1 from the control signal, and supplies the detected identification data R-1 to the memory 49 so that the identification data R-1 is written into the memory 49. If the count t of the timer 53 has reached a specified value T, for example 5 sec, the indicator/alarm 52 is activated for a short period of time to indicate that the operation mode will be switched, and then the operation mode of the signal processing unit 48 is automatically switched from the writing mode to the normal mode.
When it is required to erase all the identification data R-1, R-2, R-3 stored in the memory 49, only the switch 50-1 of the setting switch circuit 50 of the receiver 42 is first closed by operator while maintaining the other switch in the open state, and the timer 53 is started, and immediately after that, the switch 50-2 of the setting switch circuit 50 is also closed. So the operation mode of the signal processing unit 48 of the receiver 42 is set to the erasing mode.
If the switches 50-1 and 50-2 are set in the above-described manner, all the identification data R-1, R-2, R-3 stored in the memory 49 are erased. After completion of the erasing of the identification data R-1, R-2, R-3, the indicator/alarm 52 is activated for a short time so as to indicate that the contents of the memory 49 have been erased. Then the operation mode of the signal processing unit 48 automatically returns from the erasing mode to the normal mode.
The memory 49 has a plurality of (k) memory areas, so that a plurality of identification data R can be stored in these memory areas. The respective identification data R are stored in the memory 49 in such a manner that one identification data is stored in one memory area and another identification data is stored in another memory area. If k+1 or more identification data R are written, the oldest identification data R is replaced by the newest identification data R each time identification data is input.
In the conventional keyless entry system, when one of remote control transmitters 41-1, 41-2, 41-3 is lost, it is possible to erase all the identification data R-1, R-2, R-3, which are uniquely assigned to the respective remote control transmitters including the lost one, from the memory 49 of the receiver 42. This allows the keyless entry system to be excellent in security.
A basic and important requirement for the keyless entry system is that when any one of the plurality of remote control transmitters 41-1, 41-2, 41-3, for example the remote control transmitter 41-1, is lost, use of the lost remote control transmitter 41-1 can be disabled.
In the conventional keyless entry system described above, if some remote control transmitter is lost, the plurality of identification data R-1, R-2, R-3 are written in the memory 49 so that identification data are all replaced by new identification data thereby erasing the identification data R-1 assigned to the lost remote control transmitter 41-1, or all the identification data R-1, R-2, R-3 stored in the memory 49 are simply erased at the same time thereby erasing the identification data R-1 assigned to the lost remote control transmitter 41-1.
Either one of the two methods may be selected by closing the switch 50-1 of the setting switch circuit 50 of the receiver 42 or operating the switches 50-1 and 50-2 according to the predefined procedure.
However, in the conventional keyless entry system described above, to erase the identification data R-1 assigned to the lost remote control transmitter 41-1 from the memory 49, it is required to erase not only the identification data R-1 but also all the other identification data R-2 and R-3 assigned to the remaining remote control transmitters 41-2 and 41-3 by means of overwriting, because it is impossible to know which identification data is stored in which memory area of the memory 49.
After erasing the identification data R-1 assigned to the lost remote control transmitter 41-1 from the memory 49, if the lost remote control transmitter 41-1 is found somewhere, it is required to write again the identification data R-1 for the remote control transmitter 41-1 into the memory 49 to enable the use of the remote control transmitter 41-1.
However, in the conventional keyless entry system described above, when such the identification data R-1 which has been erased once is written again, it is required to rewrite all identification data R-1, R-2, R-3 for all the remote control transmitters 41-1, 41-2, and 41-3 including the remote control transmitter 41-1, although the identification data which is really required to be written is only the identification data R-1 for the remote control transmitter 41-1. Furthermore, in the conventional keyless entry system described above, if all the identification data R-1, R-2, and R-3 for the remote control transmitters 41-1, 41-2, and 41-3 are simply erased at the same time from the memory 49, it is also required to write the identification data R-1, R-2, and R-3 for all the remote control transmitters 41-1, 41-2, and 41-3 including the remote control transmitter 41-1.
As can be understood from the above description, the conventional keyless entry system has the following problems. After disabling the use of the remote control transmitter 41-1 lost, if this remote control transmitter 41-1 is found, it is required to rewrite the identification data R-1, R-2, and R-3 for all the remote control transmitters 41-1, 41-2, and 41-3 so as to enable the use of the remote control transmitter 41-1 found. However, such the rewriting process is troublesome and time-consuming.
Furthermore, the above keyless entry system needs a special setting switch circuit 50, which results in an increase in cost. Still furthermore, an unauthorized user of the car can easily operate the keyless entry system if he/she knows how to operate the setting switch circuit 50. For example, if identification data is erased with by an unauthorized person, when an authorized user of the car operates his/her remote control transmitter, the receiver 42 will not accept the control signal transmitted from his/her remote control transmitter, and therefore he/she cannot control the devices or utilities of the car. This can occur because the operation is generally common to all cars, and thus many people know how to operate the setting switch circuit 50. Furthermore, to switch the operation mode to the erasing mode, it is required to perform a further procedure in addition to the procedure of setting the operation mode to the writing mode. This causes the total operation to become complicated.
To solve the above problems, the object of the present invention is to provide a communication device capable of preventing a lost transmitter from being used by an unauthorized person and also capable of easily enabling the lost transmitter to be used again via a simple operation when the lost transmitter is found.
According to an aspect of the present invention, to achieve the above object, there is provided a communication system provided with a mode controller for switching the operation mode of a signal processing unit in a receiver from a normal mode to a control signal disable mode wherein outputting of a control signal is disabled in the control signal disable mode whereas a control signal is allowed to be output in the normal mode.
With this technique, when some remote control transmitter is lost, it is possible to disable use of the lost transmitter by switching the operation mode of the signal processing unit of the receiver from the normal mode to the control signal disable mode thereby preventing the lost transmitter from being used for a bad purpose.
Furthermore, to achieve the object described above, the communication system according to the present invention preferably includes mode setting means for selecting an operation mode depending on whether a transmission code is received or not within a predetermined period of time after a particular operation procedure.
This technique allows a user to easily switch the operation mode of the signal processing unit from the normal mode to the identification code writing mode, from the normal mode to the control signal disable mode, or from the control signal disable mode to the normal mode by performing almost the same operation procedure with a slight difference depending on the operation mode. Thus, the user can easily memorize the operation procedure. Furthermore, when the lost transmitter is found, it is possible to enable the transmitter to be used by performing a simple operation.